ebook img

Modal analysis of a robot arm using the finite element analysis and modal testing PDF

217 Pages·2016·4.33 MB·English
by  
Save to my drive
Quick download
Download
Most books are stored in the elastic cloud where traffic is expensive. For this reason, we have a limit on daily download.

Preview Modal analysis of a robot arm using the finite element analysis and modal testing

RRoocchheesstteerr IInnssttiittuuttee ooff TTeecchhnnoollooggyy RRIITT SScchhoollaarr WWoorrkkss Theses 6-1-1989 MMooddaall aannaallyyssiiss ooff aa rroobboott aarrmm uussiinngg tthhee fifinniittee eelleemmeenntt aannaallyyssiiss aanndd mmooddaall tteessttiinngg Shashank C. Kolhatkar Follow this and additional works at: https://scholarworks.rit.edu/theses RReeccoommmmeennddeedd CCiittaattiioonn Kolhatkar, Shashank C., "Modal analysis of a robot arm using the finite element analysis and modal testing" (1989). Thesis. Rochester Institute of Technology. Accessed from This Thesis is brought to you for free and open access by RIT Scholar Works. It has been accepted for inclusion in Theses by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. Modal Analysis of a Robot Arm Using The Finite Element Analysis and Modal Testing SHASHANK C. KOLHATKAR A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE in Mechanical Engineering Rochester Institute of Technology Rochester, New York June 1989 Approved by : Dr. Richard G. Budynas (Advisor) Dr. Joseph S. Torok Dr. Wayne W. Walter ....... Dr. Bhalchandra V. Karlekar (Professor and Department Head) Title of the Thesis 'Modal Analysis of A Robot Arm' I Shashank C. Kolhatkar hereby grant permission to the Wallace Memorial Library of R.I.T. to reproduce my thesis in whole or in part. Any reproduction will not be for commercial use or profit. Dated Title of the Thesis : 'Modal Analysis of A Robot Arm' I Shashank C. Kolhatkar hereby grant permission to the Wallace Memorial Library of R.I.T. to reproduce my thesis in whole or in part. Any reproduction will not be for commercial use or profit. Dated :. t/i/si Abstract The objective of the present work was to study the technique of modal analysis using theoretical and experimental methods. A PUMA UNIMATION five axis robot was used as a model. The finite element analysis was performed using MacNeai Schwendler Corporation's NASTRAN code. Intergraph's Rand Micas pre- and post-processor was used to discretize the model and subsequently to display the animated mode shapes after the analysis was done with NASTRAN. The modal testing was performed using Structural Measurement Systems' STAR software and Bruel & Kjaer's instrumentation including a spectrum analyzer, accelerometer and hammer. Due to the size and weight of the structure it was not possible to test it in its free-free condition. Hence it was tested in its supported condition. The results from the two analyses were then compared. The first thirteen modes from both the analyses showed a one-to-one correspondence. The natural frequencies showed a deviation from 1% to 33%. Although the difference of 33% seems large, it was only for one mode which could reflect a computational error. For most of the modes, the variation was less than 10%. The comparison of mode shapes was done by observation of the displayed animated mode shapes. Also, a technique called Modal Assurance Criterion for numerical correlation of mode shapes is discussed. The experimental mode shapes showed an erratic behavior. This was probably due to the nonlinearities in the structure. The causes of the discrepancies between the finite element method and modal testing are discussed in the text. Similar patterns of deflection could be seen in the two analyses. i i Acknowledgements This work is dedicated to my parents Sau. Rohini Kolhatkar and Shri. Chandrakant Kolhatkar without whose constant support and encouragement it would have not been possible to see this day in my career. I will always be grateful to you both for everything you have done for me. I also want to express my gratitude towards Maoshi and Kaka who are always there to help me when I need them! Dr. Budynas, thank you very much for seeing me through this thesis research with patience and a smile. My way of thinking is very much influenced by your in-depth, logical and systematic approach to solve problems. You will be a great source of inspiration in developing my future career. Thank you Dr.Torok and Dr. Walter for spending your valuable time reviewing my work. I really appreciate your being so understanding. My sincere thanks to Dan Foley of Bruel & Kjaer for all the help with B&K hardware I used and to our own David Hathaway for always helping me out with a smile when I got into trouble. Finally, my special thanks to all my friends for providing constant diversions when I was working. I will always cherish the memories of the past two years I spent with you. 1 1 Table of Contents Page List of Tables vii List of Figures viii List of Symbols x 1. Introduction 1 1.1 General Concepts 1 1 Motivation 3 .2 1 Modal Testing 6 .3 1 Applications of Modal Testing 7 .3.1 1 Finite Element Method 9 .4 1.4.1 Range of Applications of the Finite Element Method 10 1 Advantages of the Finite Element Method 1 1 .4.2 1 Limitations of the Finite Element Method 1 1 .4.3 1 Comparison of the Experimental and Finite Element .5 Modal Analysis 12 1.6 Mathematical Concepts 15 1 Equations of Motion for Single Degree of .6.1 Freedom System 17 1 Equations of Motion for Linear Multiple Degree .6.2 of Freedom Systems 18 1.6.3 Decoupling the Equations of Motion 21 1.6.4 Formulating the Eigenvalue Problem 23 IV Page 2. Finite Element Analysis Using MSC/NASTRAN 28 2.1 MSC/NASTRAN 28 2.2 Finite Element Modeling With NASTRAN 31 2.2.1 Executive Control Deck 31 2.2.2 Case Control Deck 32 2.2.3 Bulk Data Deck 34 2.3 Dynamic Analyis Using NASTRAN 36 2.3.1 Inverse Power Method 37 2.3.2 Given's Triadiagonal Method 39 2.3.3 Modified Givens Method 41 2.4 Dynamic Reduction 42 2.4.1 Guyan Reduction 43 2.4.2 Generalized Dynamic Reduction 45 2.5 Selection of Eigenvalue Extraction Method 48 2.6 Selection of Dynamic Reduction Method 49 3. Experimental Modal Analysis 51 3.1 Modal Analysis and Related instrumentation 51 3.1.1 Vibration Exciters 53 3.1.2 Hammer 55 3.1.3 Accelerometer 57 3.1.4 Dual Channel FFT Analzer 61 3.2 Curvefitting 62 3.2.1 Properties of the Nyquist Plot 65 3.2.2 SDOF Curvefitting 68 Page 3.2.2.1 Peak Amplitude Method 68 3.2.2.2 Circle Fit Method 71 3.2.3 MDOF Curvefitting 73 3.2.3.1 Extension of the SDOF Method 73 3.2.3.2 General MDOF Curvefitting 75 3.2.4 Autofitting 76 3.3 Modal Testing Procedure 77 4. Modeling and Results 84 4.1 Background and Assumptions 84 4.2 Procedure to Create and Analyze the NASTRAN Model 87 4.3 Finite Element Modeling of the Robot 93 4.4 Modeling for Modal Testing 102 4.5 Results of the Finite Element Analysis 103 4.6 Results of Experimental Modal Analysis 109 4.7 Comparison of Experimental and Analytical Results 115 4.8 Integration of Modal Testing and FEM 121 References 123 Appendixes Appendix A MSC/NASTRAN Cards Used in the Modal Analysis Appendix B MSC/NASTRAN Data File Appendix C Modal Testing Coordinate and Display Sequence Data Appendix D Mode Shapes from the Finite Element Analysis Appendix E Mode Shapes from Modal Testing Appendix F FORTRAN Program for 'MAC Calculations VI List of Tables Table Page 1 Comparison of the Finite Element Modal Analysis and .1 Modal Testing 13 2.1 Comparison of Dynamic Reduction Methods 50 4.1 Natural Frequency Results from Finite Element Analysis using NASTRAN 106 42 Natural Frequencies obtained from Modal Testing 113 4.3 Comparison of the Results from the Finite Element Analysis and Modal Testing 116 VII

Description:
Kolhatkar, Shashank C., "Modal analysis of a robot arm using the finite element analysis and modal testing" (1989). Thesis. Criterion for numerical.
See more

The list of books you might like

Most books are stored in the elastic cloud where traffic is expensive. For this reason, we have a limit on daily download.